Dynamic Frequency Dividers (DFD) are critical components of, for example, mm-wave (30-300 GHz) transceivers which are used, for example, in automotive radar systems. Such systems often comprises a chain of frequency dividers. A dynamic frequency divider is usually used as a first stage divider. DFDs are often based on regenerative dividers because of their high frequency performance, such as a high operative frequency and a high bandwidth.
A first example of a DFDs is disclosed in “7.3-GHz Dynamic Frequency Dividers Monolithically Integrated in a Standard Bipolar Technology”, by Rainer H. Derksen and Hans-Martin Rein, IEEE Transactions on Microwave Theory and Techniques, Vol. 36, No. 3, p. 537-541, March 1988. A second example of a DFDs for operation in the mm-wave frequency band is disclosed in “SiGe Bipolar VCO With Ultra-Wide Tuning Range at 80 GHz Center Frequency”, by Nils Pohl et al., IEEE Journal of Solid-State Circuits, Vol. 44, Issue 10, p. 2655-2662, October 2009.
FIG. 1 schematically presents the topology of the known prior art DFDs 100. A series arrangement of a transimpedance amplifier 102, a switching-quad pairs circuitry 106, and an RF-pair circuitry 110 is coupled in between voltage supply rails V+ and V−. A high frequency input signal 112 is received at input ports of the RF-pair circuitry 100 which amplifies the high frequency input signal 112 and provides an amplified high frequency signal 108 to the switching-quad pairs circuitry 106. The switching-quad pairs circuitry 106 provides a signal 104 which comprises a mixed frequencies signal to the transimpedance amplifier 102 which amplifies the received signal and provides an amplified signal 114 to two stages of emitter followers 118. An output signal 116 of the two stages of emitter followers 118 is fed back to the switching-quad pairs circuitry 106. The output signal 116 comprises a signal with a frequency that is half the frequency of the high frequency input signal 112. The switching-quad pairs circuitry 106 mixes the amplified high frequency signal 108 with the output signal 116 of the two stage of emitter followers 118. The output signal 116 of the two stages of emitter followers 118 is also provided to an output emitter follower circuitry 120 which provides the frequency divided output signal 122. The frequency divided output signal 122 has a frequency that is half the frequency of the high frequency input signal 112. The output emitter follower circuitry 120 and the two stages of emitter followers 118 are coupled between the supply voltage lines V+, V−.
FIG. 2 schematically presents a circuitry 200 of a prior art DFD. Different elements of the circuitry of FIG. 1 are indicated. The high frequency input signal 112 is received from an input amplifier circuitry. The RF-pair circuitry 110 comprises a differential pair of bipolar transistors arranged in common emitter mode, which means that each transistor receives another signal at its base, that the collectors are the output nodes of the RF pair circuitry 110 and that the emitters of the transistors are coupled to each other. The switching-quad pairs circuitry 106 comprises double differential pairs of bipolar transistors and each differential pair is arranged in a common emitter mode. The transistors of the differential pairs are coupled such that, if the bases of two transistors are coupled to the same control signal, the collector is coupled to another output terminal of the switching-quad pair circuitry 106. The combination of the RF-pair circuitry 110 and the switching-quad pairs circuitry 106 forms a Gilbert-Cell which acts as a frequency mixing circuitry. The output signal of switching-quad pairs circuitry 106 is provided to the transimpedance amplifier 102. Together with the two stages of emitter followers 118, the transimpedance amplifier 102 provides a large enough gain for operating the DFD in the mm-wave spectral range. The output emitter follower circuitry 120 acts as an additional buffer for driving further stages circuitries and prevents that the DFD feedback loop is loaded too much by the further stages circuitries.
The functioning of the prior art DFD circuits requires a relatively high voltage supply of at least 5 volts to obtain a high quality DFD for frequencies in the mm-wave band. Further, the output emitter follower circuitry 120 has to work at a relatively high current operating point in order to provide an advantageous high frequency performance. Thus, the known DFD circuit can not be used in low-voltage (for example, 3.3 volts) and low power circuits.